Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. In general, a wind turbine converts kinetic energy from the wind into mechanical energy and then subsequently converts the mechanical energy into electrical power. A horizontal-axis wind turbine typically includes a tower, a nacelle supported by the tower, and a rotor mounted to the nacelle. The rotor is coupled via a drive train to a generator housed inside the nacelle. The rotor includes a central hub and a plurality of blades (e.g., three blades) mounted to and extending radially from the hub.
A modern wind turbine has many moving parts that facilitate converting the kinetic energy of the wind into electrical energy. As such, a wind turbine typically includes many bearings that provide relative movement between adjacent parts in a relatively efficient, low-friction manner. For example, in most wind turbines the nacelle is rotatably mounted to the tower so that a yaw system may be used to control the angle of the rotor plane (i.e., the area swept by the blades) relative to the wind direction. Additionally, the blades are rotatably mounted to the hub so that a pitch system may be used to control the pitch of the blades relative to the wind direction (e.g., the blades are rotated about their longitudinal axis). Blade bearings, yaw bearings, and other bearings therefore play an important role in optimizing the operation of the wind turbine.
Bearings typically require lubrication to operate with low friction and prolong their lifetime. Most bearings in a wind turbine include first and second components, such as first and second rings, movable relative to each other. Additionally, there are often structural elements, such as roller elements or sliding pads, positioned between the first and second components. The lubrication is provided between the first and second components to reduce surface fatigue and wear. One challenge, however, is to confine the lubrication to this space so that it does not pollute or dirty other nearby components and the surrounding areas. Lubrication in unintended areas may require cleaning prior to service and maintenance operations in those areas, thereby adding time and costs to the operations. Moreover, the available space within a wind turbine is limited and access to areas is often restricted, making the cleaning itself challenging.
Most bearings include a seal to prevent leakage of lubricant. The seal is typically a rubber element positioned between the moving components of the bearing. Although such seals may be satisfactory in many situations, the potential for unintended leakage remains. The seals may wear over time, especially if rust or corrosion develops on the surfaces of the bearing rings. This may compromise the ability of a seal to confine the lubricant between the rings. Additionally, replacement of a worn seal may be difficult or even impossible without removing the bearing given the confined space of a wind turbine. Therefore, replacement may be costly and increase the downtime of the wind turbine.